This invention relates to polycarboxylic acid polymeric thickeners, especially polyacrylic acid thickeners, having improved performance under alkaline conditions. The polymeric thickener is a crossed linked carboxylic acid copolymer with an N-substituted acrylamide, such as t-butyl acrylamide, diacetone acrylamide or t-octyl acrylamide.
Polyacrylic acid polymers made by free radical, precipitation polymerization are used in a wide variety of applications especially where it is necessary to thicken water or aqueous systems. Copolymers of N-substituted acrylamides are known, but not as cross-linked polymers, for use in thickening aqueous solutions. For example, U.S. Pat. No. 4,395,524 to W. D. Emmons et al. teaches a copolymer of acrylamide and N-substituted acrylamide, which is uncross-linked, for use as flow modifiers in aqueous systems, which are also effective adsorbates from aqueous systems, particularly multiphase systems. U.S. Pat. No. 3,493,500 to Volk et al. teaches an acrylamide copolymer, with acrylic acid, which is not cross-linked, that is polymerized in an aqueous solution and that is used, e.g., as flocculents for raw sewage. British 864,311 describes the preparation and use of copolymers containing substituted acrylamides, which are not cross-linked, for use as fixatives for hair, and anti static coatings. U.S. Pat. No, 4,566,973 to W. F. Masler et al. teaches copolymers of acrylic acid and substituted acrylamide, which are not crosslinked and are used as scale inhibitors.
Crosslinked acrylic acid polymers are known, such as for example, U.S. Pat. No. 2,798,053 to H. P. Brown, which discloses acrylic acid polymerized with acrylamides, but does not teach t-butyl acrylamide and teaches polymers useful as cation exchange resins or bulk laxatives. U.S. Pat. No. 3,726,288 teaches a copolymer thickener which comprises three components, namely carboxylic acid, an amide, and a cross-linker and is also used as a fixative for setting hair. U.S. Pat. No. 4,423,199 to C. J. Chang et al. teaches a paint thickener for paint lattices, cosmetic preparations, food preparations, ionic detergents, dye paste, and oil well drilling muds, which comprises a copolymer of (meth)acrylic acid, N-substituted acrylamide, and an alkyl (meth)acrylate. An optional cross-linker is taught, but no cross-linked polymers are used in the examples.